The present invention relates generally to micromechanical systems, and more particularly to an apparatus and method for manipulating an object.
Microassembly provides the capability to construct three dimensional heterogenous Microsystems by joining sensors, actuators, structures, and intelligence. Such components are separately fabricated and ideally available off the shelf.
The problem of robotic microassembly has been explored using high precision actuators and vision feedback. Vision based approaches are limited by poor depth of field of high power microscopes, cluttered views, and lack determination of contact or contact forces. In addition, it is difficult to perform several distinct operations in parallel as microscopes are quite bulky and expensive (although parallel operations can be performed with rigid pallets and fixtures). Alternatively, force sensor based approaches can be local and provide exact information about contact between surfaces.
At the micro-scale level, adhesion forces of surface tension, and electrostatic and Van der Waals force dominate gravitational forces. Recent work has shown how adhesive forces can be used advantageously during microassembly tasks by controlling contact areas and surface tension, to ensure that microparts are reliably transferred to the target surface and released from a gripper.
Previous micromanipulation work has used a single probe or parallel jaw grippers to manipulate parts. The parallel jaw gripper approach follows from macro-robotics where a simple gripper is used with a six degree-of-freedom (DOF) arm to reorient and position parts. However, sub-centimeter six DOF micro-robot arms are not yet available.
In one aspect, the invention features an apparatus to manipulate an object. The apparatus comprises a pair of actuated compliant beams, mounted substantially perpendicular to each other, which can grip and manipulate the object.
Various implementations of the invention may include one or more of the following features. Each compliant beam includes a piezoelectric actuator. One end of the piezoelectric actuator is attached to a proximal end of a base member. A tip member is attached to a distal end of the base member. The tip member has an inclined face configured to engage the object to be manipulated. The face of the tip member may be inclined at angle of approximately 45 degrees. A strain gauge is located at a face and back of each of the base member and the tip member. The piezoelectric actuator drives a distal end of the base member. This drive is achieved through a point contact. A tip member is joined to one end of the piezoelectric actuator. Each compliant beam includes an actuator selected from the group consisting of a thermal actuator, a motor-driven beam actuator, a polymer/thermal actuator, and a flexible circuit actuator. At least one strain gauge is provided to measure a deflection of a beam or a force applied by a beam. One of the beams is only driven along a first axis, while the other one of the beams can only be driven along a second axis that is perpendicular to the first axis. Each beam is fixed to a surface.
In another aspect, the invention is directed to an apparatus to manipulate an object comprising a first arm and a second arm. The first arm is actuated only along a first axis, while the second arm is actuated only along a second axis that is substantially perpendicular to the first axis. The first and second arms define a space therebetween in which an object can be positioned such that the first and second arms can grip and manipulate the object.
In yet another aspect, the invention is directed to a system to manipulate an object. The system comprises a first arm that is actuated only along a first axis. The system further includes a second arm that is actuated only along a second axis that is substantially perpendicular to the first axis. The first and second arms define a space therebetween in which an object can be positioned such that the first and second arms can grip and manipulate the object. The system also includes an XYZ stage on which the object can be positioned.
In still another aspect, the invention features a method of manipulating an object. The method comprises grasping one side of the object with a first arm that is actuated only along a first axis and grasping another side of the object with a second arm that is actuated only along a second axis that is substantially perpendicular to the first axis. At least one of the first and second arms is actuated to manipulate the object.
Various implementations of the invention may include one or more of the following features. The first and second arms are actuated to roll the object. The first and second arms are actuated to pick and place the object. The first and second arms are actuated to reorient the object perpendicular to a grasping wall. The first and second arms are actuated to align the object along a wall.
In yet another aspect, the invention features a method of manipulating a submillimeter-sized object. The method comprises gripping one side of the object with a first actuated compliant beam and gripping another side of the object with a second actuated compliant beam that is mounted substantially perpendicular to the first beam. The first and second beams are operated to manipulate the object.
In yet another aspect, the invention is directed a method of manipulating an object comprising grasping one side of the object with a first beam that is actuated only along a first axis, and grasping another side of the object with a second beam that is actuated only along a second axis that is perpendicular to the first axis. The object is positioned in a groove in a wall as the object is grasped by the first and second beams. The position of the wall and the first beam is controlled such that the wall and the first beam grasp the object, while the second beam is transferred to another side of the object. The position of the wall and the second beam is controlled such that the wall and the second beam grasp the object, while the first beam is transferred to yet another side of the object. The wall is moved away from the object, and the first and second beams are operated to rotate the object 90 degrees.
Various implementations of the invention may include one or more of the following features. The steps of the above-described method may be repeated to rotate the object 360 degrees.
An advantage of the invention is that it enables the use of macro-scale dextrous manipulation techniques with simple mechanisms to reorient and position parts. By using gripping forces which exceed adhesion forces, Coulomb friction is used to control part sticking and sliding. Micro-parts, as well as larger parts, can be dextrously manipulated in an open-loop fashion (no feedback) using two one DOF arms in a plane combined with an XYZ cartesian stage.
Two-finger grasps of polygons and polyhedra will automatically slide to a stable configuration if the angle between the included faces is less than twice the friction angle. Conversely, a tangential force at one finger will cause the grasped part to roll about the opposite finger. As these grasping techniques do not require feedback, and are robust to initial conditions, they are well suited to the micro-domain and parallelization.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the invention will be apparent from the description and drawings, and from the claims.